Electrical motors are often placed downhole in an oil or gas field to perform a variety of functions. These functions can include artificial lift, whereby the motor drives a pump that is used to bring downhole fluids to the surface. A typical motor can be 6 inches in diameter and 30 feet long. The wire used in the windings can be ⅛ inch magnet wire. The magnet wire can be over 1000 feet long. The magnet wire is wound through the lamination stack many times to create a stator coil for each phase of the motor. The stator coils in a three phase AC motor can weigh in excess of 600 pounds.
Some designs for downhole motors use stator coils that are wrapped in polyimide tape and treated with varnish. The varnishing process provides mechanical stiffness, insulation, protects the stator coils from vibration damage, protects the coils from water, and holds the stator coils in place. The varnish itself has an upper limit operating temperature approaching 400° F. The varnish can be used in conjunction with epoxy, increasing the effective operating temperature to 550° F. At or above those temperatures the varnish will generally melt, causing the motor to be inoperable.
It is beneficial if artificial lift equipment can operate in higher temperature environments. In a steam assisted gravity drainage system a small borehole injects steam into the formation and another larger borehole below the small borehole collects the resulting production fluids. The steam is used to lower the viscosity of the well fluids and promote production of formation fluids that normally would not be possible. However, the temperature requirements for such operation can be in excess of 550° F. Therefore, a varnished stator coil can become a limiting factor when artificial lift equipment is deployed downhole in such an environment. Absent the varnish, issues can develop relating to inadequate support of the weight of the stator windings.
Accordingly, there exists a need for an apparatus and a method to retain unvarnished stator coils inside a motor housing.